During the first five centuries Seleucia in Mesopotamia,
subsequently the see of the Nestorian catholicos, was under the
Patriarchate of Antioch. In the fifth century, as can be seen in
the "Synodicon Orientale" (ed. Chabot), almost all the bishops of
Seleucia-Ctesiphon bore the title of catholicos, without, however,
severing their relations with Antioch; hence, originally, the word
catholicos was not synonymous with patriarch.
Owing to the political separation of the East from the West and to
theological disputes, several attempts were made during the fifth
century to secure religious independence. In the synod held at
Seleucia under Dadjesus in 424 (cf. Synodicon, 51, text and 296.
tr.) it was forbidden to appeal from the Catholicos of Seleucia to
the Patriarch of Antioch. The breach, however, became complete and
permanent under the Nestorian Mar Babai. The synod held under him
(497 or 499) renewed the decree of independence from Antioch, and
henceforth Seleucia became the centre of Nestorianism. The list of
the Nestorian catholicoi is given by Bar Hebraeus (Chronicon ed.
Abbeloos, and Lamy, III passim), the list is supplemented by the
editors, III, 566 sqq. In the middle of the sixteenth century, in
opposition to the Catholicos Mar Mama, several bishops met, elected
Sullaka, and sent him to Rome for consecration. Since then there
has been a Catholic patriarch whose residence is now at Mosul. A
list of the catholicoi united with Rome is given by Abbeloos and
Lamy, op. cit., 570 sqq. (See NESTORIANS)

II. ARMENIANS

Among the Armenians also catholicos was originally a
simple title for the principal bishop of the country; he was
subordinate to the See of Caesarea in Cappadocia. The bishops of
Albania and Georgia, although dependent on the Catholicos of
Armenia bore the same title. Under King Pap and the Catholicos
lousik Armenia asserted its independence of Caesarea. In the fifth
century the Armenians adopted Monophysitism and anathematized the
Council of Chalcedon, 491. Many of the catholicoi, however,
especially after the Crusades, professed the orthodox Catholic
Faith. The see of the Armenian catholicos, originally Achtichat,
has varied considerably. Besides many schisms have taken place, and
today there are no less than five Armenian catholicoi. One of them,
the successor of the old catholicos, is at Sis in Cilicia, with
jurisdiction over the Turkish provinces of Asia. His power in
ecclesiastical matters, supreme in theory, is considerably
curtailed in practice by the appointment of a catholicoi with
additional powers in Constantinople. Since 1113 there is also an
Armenian catholicos at Aghtamar with jurisdiction over the island
of that name and the villages surrounding Lake Van. Another
catholicos resides in Jerusalem, but with greatly reduced powers.
In 1441 another schism occurred, and a catholicos was elected in
Etchmiadzin in Greater Armenia. Today he bears the title of
"Supreme Patriarch and Catholicos of all Armenians" and at least
theoretically, is considered the principal catholicos by all
non-Catholic Armanians. Since 1740 there has also been a Catholic
catholicos in Constantinople with the title of Patriarch of
Cilicia. He is recognized by the Porte as having jurisdiction over
all Catholic Armenians in the Turkish possessions. (See ARMENIA;
CONSTANTINOPLE.)

In the beginning of the fourth Century Albania and Georgia
(Iberia) were converted to Christianity by Armenian missionaries,
and the principal bishop of each of these countries bore the title
of catholicos, although neither of them was autocephalous. They
followed the Armenians in rejecting the Council of Chalcedon. At
the end of the sixth, or beginning of the seventh, century the
Georgian catholicos asserted his independence and came back to
orthodoxy. Henceforward the Georgian Church underwent the same
evolutions as the Greek. In 1783 Georgia abolished the office of
its catholicos, and placed itself under the Holy Synod of Russia,
to which country it was united politically in 1801. The Albanian
catholicos remained loyal to the Armenian Church, with the
exception of a brief schism towards the end of the sixth century.
Shortly afterwards Albania was assimilated partly with Armenia and
partly with Georgia. There is no mention of any catholicos in
Albania after the seventh century. It is asserted by some that the
head of the Abyssinian Church, the Abuna, also bears the title of
catholicos, but, although this name may have been applied to him by
analogy, there is, to our knowledge, no authority for asserting
that this title is used by the Abyssinian Church itself.